1. Field of the Invention
The present invention relates to a chucking device in an FDD (floppy disk drive) capable of effecting centering easily and accurately at the time of loading a floppy disk into the FDD.
2. Description of the Related Art
A recording medium, typical of which is a floppy disk, is loaded into an FDD in the form of a disk cartridge in which a thin film-like recording disk is received in a case, the recording disk is rotated within the FDD, and recording data are inputted and outputted through a write/read window formed in the case and having a shutter. It is necessary that the recording disk be capable of being removed easily in its received state in the case and aligned exactly with a rotational axis of the FDD at the time of write or read and that the rotating speed thereof be controlled accurately. To meet these requirements, such a chucking device as shown in FIGS. 6 and 7 has heretofore been used for the FDD.
A center hub formed by a ferromagnetic metal disk is centrally mounted on a recording disk of a floppy disk. As shown in FIGS. 6 and 7, a generally square central aperture 3 is formed centrally of the center hub which is indicated at 2, and a generally rectangular drive pin aperture 4 is formed in a peripheral position of the center hub. The drive pin aperture 4 has a front edge 4a at a front position in a rotational direction of a rotor yoke and an outer edge 4b in a direction ("outer" hereinafter) away from a rotational center of the rotor yoke.
On the other hand, the FDD is provided with a rotor yoke 101 which is constituted by a ferromagnetic metal disk and which is rotated in a certain direction (indicated at "D" in the figures) by means of a motor (not shown). A magnetic disk (chucking magnet) 102 is held in place on the rotor yoke 101 through a boss and a boss hole and is attracted magnetically.
A center shaft 103 is erected at a rotational axis O of the rotor yoke 101. The center shaft 103 extends through a central opening 102a of the magnetic disk 102 and is inserted loosely into the central aperture 3 of the center hub.
The term "loosely" as used herein indicates a freely movable state in both horizontal and vertical directions and within a predetermined range.
In the peripheral portion of the rotor yoke 101 is formed a drive pin through hole 104 along the circumference, and a chucking arm 105 formed arcuately along the circumference is loosely fitted in the drive pin through hole 104. An upwardly extending drive pin 106 is formed at a front end portion ("front portion" hereinafter) 105a of the chucking arm 105 facing the rotational direction D of the rotor yoke 101. The drive pin 106 extends loosely through a front aperture 102b formed in the magnetic disk 102 and is inserted loosely into the drive pin aperture 4 of the center hub. At the front portion 105a of the chucking arm 105 are formed two flanges 105c which hold loosely the rotor yoke 101 portion located around the front portion of the drive pin through hole 104 and which support the front portion of the chucking arm 105 so as to be freely movable in both horizontal and vertical directions and within a predetermined range.
On the other hand, the other end portion ("rear portion" hereinafter), indicated at 105b, of the chucking arm 105 extends backward of the upper surface of the rotor yoke 101 at an approximately right angle from the rear end of the drive pin through hole 104, and within a rear aperture 102c formed in the magnetic disk 102 a pivot shaft 108 projecting from the upper surface of the rotor yoke 101 is received in a receiving aperture 105d so as to be pivotable horizontally about the pivot shaft 108 and within the width range of the drive pin through hole 104.
A ferromagnetic plate 109 is mounted on the body of the chucking arm 105, whereby the whole of the chucking arm 105 is attracted magnetically by the magnetic disk 102 and the drive pin 106 is pulled upward at all times.
Upon loading of a floppy disk into the FDD constructed as above, the recording disk is placed on the rotor yoke 101, the center hub 2 mounted on the disk is attracted magnetically by the magnetic disk 102, and the central aperture 3 of the center hub receives the rotor yoke-side center shaft 103 therein. At this time, the drive pin 106 projecting upward from the magnetic disk 102 need not be inserted into the drive pin aperture 4 of the center hub. With the drive pin 106 not inserted into the drive pin aperture 4, the pin 106 is pushed in by the center hub 2 up to the lower surface level of the center hub against the attractive force induced by the ferromagnetic plate 109.
In this state, when a motor (not shown) is turned ON, causing the rotor yoke 101 to rotate fully once at most in the D direction, the top of the drive pin 106 slides and rotates on the lower surface of the center hub and is received in the drive pin aperture 4, within which the drive pin rises by virtue of the attractive force of the ferromagnetic plate 109. As the rotor yoke 101 further rotates in the D direction in this state, the chucking arm 105 moves pivotally in a direction in which the drive pin 106 moves away from the rotational axis O of the rotor yoke 101 under the action of a centrifugal force induced by the rotation of the rotor yoke 101, and the drive pin 106 comes into abutment with the outer edge 4b of the drive pin aperture 4. At the same time, the drive pin 106 slides forward within the drive pin aperture 4 by virtue of the rotational force of the rotor yoke 101 and come into abutment also with the front edge 4a of the drive pin aperture 4. As a result, the drive pin 106 is supported in abutment with the two sides of the front and outer edges 4a, 4b of the drive pin aperture 4. This state will hereinafter be referred to as "front-outer support."
At this time, the center shaft 103 is supported by being abutted against two adjacent sides 3a and 3b of the central aperture 3 of the central hub on the side opposite to the drive pin 106 with respect to the rotational axis O and in this state the center of the recording disk and the rotational axis O of the rotor yoke 101 coincide with each other to complete chucking. In this state the recording disk of the floppy disk can rotate while exactly following up a controlled rotating speed of the rotor yoke 101.
The above conventional chucking device uses the chucking arm 105 for attaining the front-outer support for the drive pin 106. However, since the chucking arm relies for the front-outer support on only the swing motion based on the centrifugal force of the arm, there sometimes occurs a case where the swing motion stops with the drive pin 106 not in abutment with the outer edge 4b due to, for example, a sliding resistance induced between the arm and the rotor yoke and the recording disk shifts directly to a continuous rotation. In this state, the rotation of the recording disk will be eccentric because the normal front-outer support position is not reached yet. Such an eccentric rotation gives rise to the problem that there occurs an error in writing and reading of data.
There has also been the problem that the mounting of the chucking arm 105 is troublesome and that therefore the manufacturing cost increases.